A light emitting diode (LED) is a semiconductor device that emits various lights depending on recombination of electrons and holes at a junction of p-type and n-type semiconductors when a current is applied.
A light emitting diode, which is a III-V nitride-based semiconductor device, has started from a lateral (or horizontal) structure and has been developed toward a flip-chip and vertical structure for high-luminance characteristics. In particular, vertical LEDs are being actively developed to achieve high-luminance characteristics under the high-power/high-temperature circumstance such as vehicle lighting application.
An LED structure formed of GaN constitutes a lateral structure and a flip-chip and vertical structure. Characteristics that should be commonly secured in these LEDs irrespective of individual structure and shape are low non-contact resistance, uniform current spreading, efficient heat diffusion, photon extraction efficiency, and the like.
In general, semiconductor light emitting diodes may be classified into a light emitting diode (LED) and a laser diode (LD). In particular, a light emitting diode and a laser diode commonly have a p-n junction where light, i.e., photon is generated when forward bias current flows. In particular, the key point of a light emitting diode using a III group nitride-based material is to enhance light extraction efficiency.
When current is applied to a p-n junction structure of a light emitting diode, light is generated at an activation layer between a p-type semiconductor and an n-type semiconductor.
In the case of a horizontal light emitting diode, to form an n-electrode, an n-type semiconductor layer is exposed by means of dry mesa etching to form a mesa structure. In this case, a large amount of activation layer is removed. A study is required to overcome this disadvantage.
Since current in the horizontal light emitting diode does not uniformly spread, local light emission occurs, which is called current crowding. Another study is required to overcome the current crowding.